Question

A 52 year old nearsighted person wears a glass with the power of minus 5.5 diopters for his distance viewing his doctors prescribe a correction of + 1.5 diopters in the near vision for his bifocals . this is measured relative to the main part of the lens .
what is the focal length of his distance viewing part of the lens ?
what is the focal lens office near vision section of the lens ?

Answer 1

Dear Student,
Please find below the solution to the asked query:

Since we know that 
power of a lens = 1/focal length(in metres)
(a)
-5.5 = 1/f
f = -1/5.5
f = -0.1819 m
f = -18.19 cm

(b)
for near vision
+1.5 = 1/f
1.5 = 1/f
f = 1/1.5
f = 0.6667 m
f = 66.67cm


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smartAbhishek ..........

Answer 2

66.67m. is your answer